The invention relates to a service architecture for a telecommunication network, in particular, an Integrated Services Packet-Switched Networks which makes it possible to support different applications requiring different levels of quality-of-service (QoS).
The current trend of integrating communication networks requires the development of network architectures that are capable of supporting the diverse range of quality-of-service needs that are required for a diverse range of different applications. Applications differ in the traffic they generate and the level of data loss and delay they can tolerate. For example, audio data does not require the packet-error reliability required of data services, but audio data cannot tolerate excessive delays. Other applications can be sensitive to both data loss and delay.
The network architectures under consideration are based on the packet (or cell) switching paradigm, for example Transmission Control Protocol/Internet Protocol (TCP/IP) or Asynchronous Transfer Mode (ATM). The basic idea behind integrated services packet-switched networks is that all traffic is carried over the same physical network but the packets belonging to flows with different QoS requirements receive different treatment in the network. A flow represents a stream of packets having a common traffic (e.g. peak rate) and QoS (e.g. loss) description, and also having the same source and destination.
This differentiation in treatment is generally implemented by a switch mechanism that first classifies packets arriving at a Switching Node (SN) according to their QoS commitment, and then schedules packets for transmission based on the result of the classification. Ideally, the classifier and scheduler in each switching node should be simple, fast, scalable and cheap.
In order to protect existing commitments, the network must be able to refuse any new request. This is accomplished using Admission Control (AC) during which some mechanism (usually distributed) decides whether the new request can be admitted or not.
Among the several proposed solutions to the problem, they can be categorised into two main groups depending upon whether or not they have what is known as xe2x80x9cper-flowxe2x80x9d scheduling.
FIG. 1 shows a known solution based on per-flow scheduling. This type of system has a scheduling algorithm which maintains a per-flow state, and the amount of work to be done depends on the number of the flows. A dynamic queue/memory handler 13 assigns a separate buffer Q1 to Qn for each flow. Each different source provides a descriptor of its traffic in advance, limiting the amount of load sent into the network. The network decides using admission control 12 whether it should accept a new request. After admission, an edge device, (being a function on the boundary of a trusted region of a service provider which acts as a checking point towards another service provider or subscriber), polices the traffic of the source. A typical example of the policing used is Weighted Fair Queuing (WFQ) or similar variants.
Solutions which use this form of per-flow scheduling have the disadvantage of requiring complex queue handlers and classifying/scheduling hardware. For each packet, the classifier 10 must determine the corresponding buffer Q1 to Qn that the packet should be put into. The large and variable number of queues means that the queue handler""s function is complex. When the next packet is to be sent, the scheduler 14 must select the appropriate buffer to send from. The scheduler 14 can also be a bottleneck due to the large number of queues it must service. The per-packet processing cost can be very high and increases with the number of flows. In addition, the algorithms are not scalable, which means that as the volume and the number of flows increases, the processing complexity increases beyond what can be handled.
FIG. 2 shows another known solution based on a system where there is no per-flow scheduling. This type of solution provides some fixed, predefined QoS classes. The scheduling is not based upon the individual flows but on the QoS class of the packets. This type of method requires simpler hardware. A separate queue Q1 to Qn is provided for each QoS class. The packet classifier 15 classifies the incoming packets into the appropriate QoS queue, Q1 to Qn. This solution either tries to ensure better service to premium users, or explicit deterministic guarantees.
Proposed solutions which do not use per-flow scheduling have one of two limitations. First, they are able to provide only very loose QoS guarantees. In addition, the QoS metric values are not explicitly defined, (e.g. differential services architectures). Secondly, the provided guarantees are deterministic, which means that no statistical multiplexing gain can be exploited. As a result, the network utilisation is very low.
The aim of the present invention is to overcome the disadvantages of the prior art listed above by providing a service architecture having a simple and scalable way to guarantee different levels of quality-of-service in an integrated services packet-switched network. This is achieved using switching nodes that combine simple packet scheduling and measurement based admission control to provide explicit quality-of-service guarantees.
According to a first aspect of the present invention, there is provided an admission control method for a switching node of an integrated services packet-switched network, the method comprising the steps of:
allocating each incoming flow to a respective selected one of the plurality of priority levels, based on service guarantees required by said flow;
determining whether, if the incoming flow is admitted, the service guarantees can be met for the incoming flow and all previously admitted flows; and, if so,
admitting the incoming flow.
According to another aspect of the invention, a switching node comprises:
means for allocating each incoming flow to a respective one of the priority levels, based on service guarantees required by said flow;
admission control means for determining whether, if the incoming flow is admitted, the service guarantees can be met for the incoming flow and all previously admitted flows; and,
means for admitting the incoming flow if this is so.
According to a further aspect of the invention, an integrated services packet switched network comprises a plurality of switching nodes, wherein at least one switching node comprises:
means for allocating each incoming flow to a respective one of the priority levels, based on service guarantees required by said flow;
admission control means for determining whether, if the incoming flow is admitted, the service guarantees can be met for the incoming flow and all previously admitted flows; and,
means for admitting the incoming flow if this is so.